Power storage system with low voltage and high voltage windings for a vehicle driving system

ABSTRACT

The invention relates to a power storage system intended to transmit power to and from a driving system of a vehicle. A power storage having a stator provided with two windings and at least one rotor provided with a magnetic-flux generating device is comprised. The rotor is connected to a flywheel intended for storage of energy. The two windings of the stator are arranged for high and low voltage, respectively. The power storage is arranged to transmit power to and from the electric apparatus as well as store energy transmitted from the electric apparatus in the flywheel.

This application is a U.S. National Phase of International PatentApplication Ser. No. PCT/SE2003/001780, filed Nov. 17, 2003 which claimspriority to Swedish Patent Application No. 0203434-6 filed Nov. 18,2002.

TECHNICAL FIELD OF THE INVENTION

The present invention relates to a power storage system intended tostore and transmit power to and from a driving system of a vehicle. Thesystem comprises a power storage having a stator provided with windingand at least one rotor provided with a magnetic-flux generating device.The rotor is connected to at least one flywheel intended for storage ofenergy in the form of kinetic energy in at least one rotary mass. Thedriving system comprises an electric apparatus, the power storage beingarranged to transmit power to and from said electric apparatus.

BACKGROUND ART

Power storage systems having a flywheel that is charged by a drivingobject and subsequently serves as source of power for, e. g., anelectric motor is used, inter alia, in driving systems such as adriveline of a vehicle. However, known systems are limited, the energystorage capacity is limited by many factors such as the weight of thesystem, security requirements, the availability of suitable materials aswell as the availability of suitable driving systems for the rechargingof the flywheel and for the discharging of the same. In a driveline in ahybrid vehicle, an energy storage is found, which, e.g., may be abattery and/or a fuel tank, an electric drive motor and/or an internalcombustion engine.

To be able to make use of the energy at retardation of a vehicle, forinstance an automobile or a train, a fast system that manages totransmit and store high powers is required. The stronger the retardationis, the higher power the system has to be able to handle in order tomake use of the energy.

A known system for storage of kinetic energy is shown in U.S. Pat. No.5,931,249. The system described according to the document comprises aflywheel, intended for accumulation and discharging of energy,respectively, which is coupled to an electric apparatus operating asmotor and generator, respectively, depending on whether energy is fed toor from the flywheel. When the system is used in a vehicle, duringshorter periods of time the vehicle may be driven from the flywheel. Theflywheel rotates at a high speed in vacuum. Together with the systemdescribed, high currents are required, which results in high losses ifhigh power is to be handled. Thus, the known system is not suitable forhigh powers.

Today's batteries are limited in respect of the power that they manageto carry. This entails that the charging time for battery-poweredvehicles generally amounts to several hours. A battery-powered vehiclecannot be driven more than a limited range before the vehicle has to bebrought to a recharging station and there be recharged during arelatively long time before the vehicle again has a certain range,frequently in the range of 100 km.

BRIEF DESCRIPTION OF THE INVENTION

The invention according to the present application is intended toprovide a power storage system intended for storage and discharging ofenergy in a driving system of a vehicle that solves the above-describedproblems. The system comprises a power storage having a stator providedwith two windings and a rotor provided with a magnetic-flux generatingdevice. The first winding of the stator is intended for low voltage forthe transmission of energy of low power, while the is second winding isintended for high voltage for the transmission of high power. The rotoris connected to a flywheel intended for storage of kinetic energy in atleast one rotary mass. The power storage system is arranged to transmitpower in both directions between the power storage and an electricapparatus comprised in the driving system. By choosing to provide thestator with a high-voltage winding, very high power can be transmittedin both directions in the system. Thanks to this, the system becomesvery fast and manages to handle the power that is developed during fastdynamical processes.

With low voltage is meant voltage below 380 V and with high voltage ismeant voltage above 380 V.

In a preferred embodiment, said first winding is arranged to operate ata voltage that is in the interval of 6-50 V.

In a further, preferred embodiment, said second winding is arranged tooperate at a voltage that is in the interval of 1-24 kV.

In a further, preferred embodiment, at least one of said windingscomprises a conductor surrounded by a first semiconducting layer, saidfirst semiconducting layer is then surrounded by a layer of fixedinsulation, said first layer of fixed insulation is then surrounded by asecond semiconducting layer. By means of a winding having this type ofinsulation system, a very high power can be transmitted.

In a further, preferred embodiment, in said driving system an energystorage is comprised, which may be a battery, that is connected with theelectric apparatus of the driving system. Power may be transmitted fromthe power storage to the energy storage and vice versa. By arranging thewindings in the stator in such a way that they are controlled entirelyindependently of each other, at every instant a battery in a drivingsystem can be utilized in an optimal way regarding discharging andrecharging. In a hybrid vehicle being driven in the position of batteryoperation thereof, i.e. when the fuel engine of the vehicle is not used,for instance during driving of a bus in an urban environment, fastprocesses that require high power can be regulated via the powerstorage/flywheel while continuous energy is fed to the driving systemvia the battery of the vehicle during battery operation. Thus, at fastand strong retardations energy is fed to the flywheel for accumulationand is fed out therefrom when power requirement is at hand, as, forinstance, at variations of torque or demands of quick acceleration ofthe vehicle.

Further, by the fact that both windings of the stator are intended tooperate at high and low voltage, respectively, the system enables energyto be fed very fast to and from the flywheel via the high-voltagewinding, as energy to and from the battery is fed with appropriatevoltage via the low-voltage winding of the stator. The windings operateentirely independently of each other, and therefore the load of thebattery can be adapted in a way that is favorable to the condition andservice life of the battery. Then, at every instant the battery canoperate in a way being appropriate to the battery, while fast andpower-demanding variations of operation such as accelerations and strongretardations, are managed via the flywheel and the high-voltage windingof the stator, which enables quick transmission of energy in a veryshort time to and from the flywheel of the system.

In a preferred embodiment, the flywheel is charged with energy that hasbeen transmitted from an external source. In a battery-powered vehicle,by utilizing a driving system having a power storage system according tothe present invention, the battery of the vehicle can, on one hand, berecharged in a conventional way at a recharging station, and theflywheel can, on the other hand, be charged maximally with energy.During operation, the energy accumulated in the flywheel may then beused for the propulsion of the vehicle, thereby increasing the range ofthe vehicle considerable, or alternatively the energy may be used forcontinued recharging of the battery of the vehicle. In this way, thebattery may be charged continuously during a longer period of time,while the downtime at the recharging station yet becomes considerableshorter.

In a preferred embodiment, said magnetic-flux generating device in therotor comprises permanent magnets,

In another preferred embodiment, said magnetic-flux generating device inthe rotor comprises a squirrel cage winding.

In a further, preferred embodiment, said rotor is mounted with magneticbearings.

The rotor is, in a further, preferred embodiment, mounted with bothmagnetic bearings and sliding bearings.

In a further, preferred embodiment, said stator is air-gap wound.

In a further, preferred embodiment said power storage is gyro suspended.By choosing a gyro suspended power storage, the driving properties ofthe vehicle will only be affected on a small scale.

In a further, preferred embodiment, said flywheel comprises at least tworotary masses that are arranged to rotate in opposite directions ofrotation in relation to each other. By using counter-rotating masses,the forces that arise in the system at rotation of the same areminimized.

In a further, preferred embodiment, said rotor comprises a first core, asecond core as well as a third core. The first winding is arranged inthe air gap between the first and the second core and the second windingis arranged in the air gap between the second and the third the core. Bymeans of this configuration, the first and the second winding aremagnetically disconnected from each other and can thereby operateentirely independently of each other.

The system according to the present invention may be used together withany vehicle, for instance automobile, train, aeroplane, boat. Theabove-described system has high efficiency, above 90%, and reacts veryfast, in the range of a few milliseconds. The system is compact, robustand durable, which is a prerequisite for use in severe environment,which is the case in most types of vehicles. The system manages togenerate and absorb high powers.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a driving system of a vehicle having a power storage systemaccording to the present invention.

FIG. 2 shows a further driving system of a vehicle having a powerstorage system according to the present invention.

FIG. 3 shows a power storage that is comprised in the system accordingto the present invention.

FIG. 4 shows an embodiment of the stator comprised in the power storage.

FIG. 5 shows an embodiment of a winding.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

FIG. 1 shows a power storage system according to the present invention.A power storage 20 having a stator 24 and a rotor 21 that is connectedto a flywheel 22 is—via a first converter 10, a direct currenttransmission 13 and a second converter 11—arranged to transmit power toand from an electric apparatus 12. The flywheel 22 comprises a rotarymass 23. When power is transmitted from the electric apparatus 12 to thepower storage 20, which, for instance, is the case at retardation of anelectrically driven vehicle, the apparatus 12 operates as generator andpower is transmitted from the apparatus 12 via the converter 11, thedirect current transmission 13 and the converter 10 to a winding (notshown in figure) comprised in the stator 24 and is then stored in theflywheel 22 in the form of kinetic energy in the rotary mass 23. Thekinetic energy stored in the rotary mass 23 may subsequently, ifrequired, be correspondingly transmitted to the electric apparatus. Thenthe electric apparatus operates as motor. This system may be used in thedriveline of a vehicle, and the power storage 20 is then used both aspower buffer and energy buffer. The stator comprises two windings, withthe first winding being intended for low voltage for the transmission ofenergy of low power, while the second winding is intended for highvoltage for the transmission of high power. The stator's winding inwhich high power is transmitted is arranged to operate at high voltageover 380 V, preferably in the interval of 1-24 kV. By said arrangement,very high power can be transmitted to and from the power storage 20.Thanks to this, the system manages to handle the high powers that ariseat, for instance, strong retardations.

FIG. 2 shows a system having an energy storage 14 that may be a battery,a fuel cell, or other chemically stored energy such as a fuel tank of aninternal combustion engine, and a power storage 20 comprising a stator24 and a rotor 21 connected to a flywheel 22 having a rotary mass 23.The stator 24 is provided with a first and a second winding (not shownin figure). The respective windings are arranged to operate at lowvoltage and at high voltage, respectively. With low voltage is meantvoltage lower than 380 V and with high voltage is meant voltage higherthan 380 V. The rotor 21 is provided with a suitable magnetic-fluxgenerating device such as, for instance, permanent magnets or aninduction winding. The flywheel 22 is intended for accumulation andquick transmission of power to and from the driving system. Further, thepower storage system comprises two converters 10 and 11 having anintermediate direct current transmission 13. One of the converters,converter 11, is arranged in connection with an electric apparatus 12.As in the system shown in FIG. 1, the electric apparatus 12 operateseither as motor or as generator depending on present mode of operation.At retardation of a vehicle provided with this system, the apparatus 12operates as generator and the generated power is transmitted via theconverter 11 and the direct current transmission 13, which can operateat high voltage as, e. g., 1.2 kV, via the converter 10 to thehigh-voltage winding of the stator and further to the power storage 20,where the energy is stored in the form of kinetic energy in the rotarymass 23 of the flywheel. By the fact that the power is transmitted athigh voltage from the high-voltage winding of the stator, high powers,such as braking power at strong retardation of a vehicle, can be madeuse of and stored. The power accumulated in the flywheel maysubsequently be used in fast processes, such as variations of torque orquick acceleration of a vehicle, when the energy from the flywheel canbe brought back very fast to the driving system via the high-voltagewinding of the stator. Alternatively, in the case where the energystorage 14 consists of a battery, the energy stored in the flywheel maybe used to recharge the battery. Then, the energy is transmitted at lowpower and low voltage to the battery via the low-voltage winding of thestator.

FIG. 3 shows a power storage of the type that is comprised in both ofthe above-described systems according to FIGS. 1 and 2. The rotor 21 ismounted with a journal bearing 25 and a guide bearing 26, respectively.The bearings may be conventional bearings or magnetic or a combinationof magnetic bearings and sliding bearings. The rotor 21 is connected toa flywheel 22 provided with a rotary mass 23. Further, the power storagecomprises a stator 24 provided with a first and a second winding (notshown in figure). During operation, power is transmitted between thestator 24 and the rotor 21, and thereby the flywheel 22 having therotary mass 23, via one of the windings of the stator.

FIG. 4 shows an embodiment of an air-gap wound stator 24. A firstwinding 31 is arranged between first and second cores 32, 33 arranged inthe rotor. A second winding 31 is arranged between the second core 33and a third core 34 arranged in the rotor. By means of thisconfiguration, the first winding 30 and the second winding 31 aremagnetically disconnected from each other and can, thereby, becontrolled entirely independently of each other. The arrows 35 show thedirection of the magnetic field.

The stator and rotor of the power storage may be arranged to operatewith either radially or axially directed magnetic flux.

The invention is not limited to the above embodiments given as examples,but may be made as modifications within the scope of the general ideaaccording to the invention described in the appended claims.

In a further, preferred embodiment, at least one of said windings 30,31comprises a conductor 40 surrounded by a first semiconducting layer 42,said first semiconducting layer 42 is then surrounded by a layer offixed insulation 44, said first layer of fixed insulation 44 is thensurrounded by a second semiconducting layer 46. By means of a windinghaving this type of insulation system, a very high power can betransmitted.

1. A power storage system which transmits power to and from a vehicledriving system the system comprising: a vehicle driving systemcomprising at least one electric apparatus, a power storage coupled tothe electric apparatus and having a stator-provided winding and at leastone rotor provided with a magnetic-flux generating device, said rotorbeing connected to at least one flywheel intended for storage of energyin the form of kinetic energy in at least one rotary mass, said powerstorage being arranged to transmit power to and from said electricapparatus, wherein said stator comprises at least a first windingarranged to transmit power to and from the electric apparatus at avoltage that is in the interval of 6 to 50 volts as well as a secondwinding arranged to transmit power to and from the electric apparatus ata voltage that is in the interval of 1 to 24 kV, said first and secondwindings being arranged to operate independently of each other, whereinat least one of said windings comprises a conductor surrounded by afirst semiconducting layer, said first semiconducting layer is thensurrounded by a layer of fixed insulation, said first layer of fixedinsulation is then surrounded by a second semiconducting layer whereinsaid rotor comprises a first core, a second core as well as a thirdcore, the first winding of the stator being arranged between said firstand said second core and the second winding of the stator being arrangedbetween said second and said third core.
 2. Power storage systemaccording to claim 1, wherein at least one energy storage is comprised,which energy storage is connected with said electric apparatus, saidpower storage being arranged to transmit power to and from said energystorage.
 3. Power storage system according to claim 1, wherein saidpower storage is arranged to receive power that has been transmittedfrom an external source.
 4. Power storage system according to claim 1,wherein said magnetic-flux generating device in the rotor comprisespermanent magnets.
 5. Power storage system according to claim 1, whereinsaid magnetic-flux generating device in the rotor comprises a squirrelcage winding.
 6. Power storage system according to claim 1, wherein saidrotor is mounted with magnetic bearings.
 7. Power storage systemaccording to claim 6, wherein said rotor also is mounted with slidingbearings.
 8. Power storage system according to claim 1, wherein saidstator is air-gap wound.